[FooBarWidget]

> I understand that you want to offer something that 'beats' varnish, and it shines through in the article.

I am the author of the article. No, the point is not to "beat" Varnish. It is an article describing various ideas and a call for help. See https://news.ycombinator.com/item?id=8844905

Perhaps the writing style gave a competitive impression, so I've updated the article to mention that we're not out to beat Varnish, but to research the possibilities.

Knowing that Varnish can accomplish some of the things is good, because that way we can draw from an existing pool of experience.

[cheald]

Everything described in the article is covered by Varnish. You can hash on Vary headers, on individual cookie values, on the sum of the digits in the user's IP address if you want. ESI lets you provide partial caching of pages as the article describes - it's actually a separate standard that's existed since 2001 (http://en.wikipedia.org/wiki/Edge_Side_Includes).

Varnish also gives us things like ACLs for managing access to various resources, on-demand content purges, multiple routable backends with different cache/grace rules, and more powerfully, request pre-processing - one thing we do is process the request and determine if the agent is capable of accepting WebP images, and if they are, we add that to the hash key with a corresponding header for the app to key on and determine whether to serve JPEG or WebP images. This lets us serve WebP images to modern agents for faster downloads, while gracefully falling back to JPEG for anything we're not sure of.

Varnish is way more than a "make Wordpress not destroy your server" cache.